The photon detection efficiency (PDE) and timing performance of silicon photomultipliers (SiPMs) need to be improved for various applications, including time-of-flight positron emission tomography, light detection and ranging, and high-energy physics experiments. However, the irradiation of some incident photons to the low-photosensitivity areas of the SiPM negatively affects its PDE and timing performance. In this study, we developed a 40 × 40 metalens array to focus incident photons on the photosensitive area of the SiPM, thereby improving the PDE and timing performance. As a proof of concept, we experimentally investigated the effectiveness of this method. After characterizing the fabricated metalens, we found that the focused beam size is approximately 1 μm (full width at half-maximum) at the optimal focal plane. Furthermore, we demonstrated the effectiveness of the metalens in significantly improving the PDE (within a 5.8 σ confidence level) and timing performance (within a 3.0 σ confidence level). The results demonstrate the potential for using metalenses for versatile applications of SiPMs.

Improving the SiPM performance, such as photon detection efficiency (PDE) and timing resolution, is key to high-accuracy measurements for these applications.A SiPM typically contains trench areas, which are located between the boundaries surrounding SPADs, to shield from optical crosstalk. However, trenches can be photo-insensitive areas. Thus, incident photons impinging the trench areas cause PDE degradation. To solve this problem, microlenses are commonly integrated with SPADs to guide the incident photons toward their photosensitive area. [10,11] The recent trend toward miniaturization of the SPAD has led to the development of a complex photosensitive area because electrode patterns and trench areas must be formed in a limited space. However, the fabrication of complex-shaped microlenses has been challenging. Furthermore, precise alignment between microlenses and small state-of-the-art SPADs has been technically difficult because microlenses are incompatible with the CMOS process.On the other hand, metalenses, [12][13][14][15][16][17][18] such as 2D sub-wavelength structures, are highly flexible in shape and size, and can be designed to focus incident photons on the complex and small photosensitive areas of SPADs. [19,20] In addition, metalenses can be easily integrated with such SPADs without alignment errors owing to their 2D ultrathin structure and suitability for CMOS processes. Based on these advantages, we introduce a monolithic metalens integrated with SPAD rather than using microlenses.Our previous study demonstrated that metalenses can improve the PDE and timing performance of the SiPM by focusing the incident photons toward the photosensitive area of the SPAD while avoiding illumination to the trench area. [21] However, as the metalens and SiPM are spatially separated, it is difficult to fix the relative position (e.g., tilt, distance, and alignment) between the metalens and the SiPM. Thus, a separate configuration is not practical. A metalens should be monolithically integrated with its corresponding SPAD to provide good alignment and stable performance enhancement while maintaining the miniaturization and flatness of the optical device, which benefits practical applications.A 300-µm-thick support glass or protection resin is typically mounted on a SiPM to protect its surface. [22] However, when metalenses are formed on the support glass, the propagation Silicon photomultipliers (SiPMs), consisting of 2D single-photon avalanche diode (SPAD) arrays, have been widely used in many applications. In a SiPM, trench structures surround every SPAD to minimize optical crosstalk; however, these structures are photo-insensitive areas. The previous study revealed that the use of metalenses for focusing incident photons on the photosensitive area of SPADs effectively improves the SiPM performance. However, ensuring good alignment between the metalens and SiPM has been difficult owing to its separated configuration. Herein the authors report the monolithic integration of a metalens with SPAD to provide stable pho...

The continuous downscaling of electronic devices requires higher-resolution optical microscopic images for semiconductor failure analysis (FA). However, a part of the diffracted light from the measuring pattern in the silicon (Si) substrate cannot be collected due to the total internal reflection (TIR) at the interface between the Si substrate and air. We propose a metalens suitable for FA that improves resolution of optical microscopic images by collecting beyond the critical angle of TIR at the interface. For the proof of concept, we integrated the fabricated metalens into the optical setup of FA and acquired optical microscopic images of FA that clearly show improved resolution.

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Barium fluoride, an inorganic scintillation material used for the detection of X-ray and/or gamma-ray radiation, has been receiving increasing attention in the field of radiation measurements in fast-timing applications. To make full use of its timing properties, its slow emission around the ultraviolet region, more specifically, the 300 nm region needs to be suppressed. Although doping ions, such as lanthanum, yttrium, and cadmium, can suppress the slow component, such techniques can lose information of interacted radiations. Consequently, a suppression technique that does not suffer from information loss while maintaining precise timing measurements would be desirable. In this study, we proposed aluminum nano-disk-based plasmonic filters to suppress slow emissions while maintaining fast emissions around 195 and 220 nm and a usability of the slow component. Finite-difference time-domain simulations and experimental results exhibited good agreement, with over 90% of slow components being adequately suppressed without sacrificing fast components, proving that aluminum nanodisks can be used for ultraviolet filters. Moreover, based on the designed filter performance, we conducted coincidence time resolution simulations for positron–electron annihilation gamma rays from an analytical perspective. The simulations indicated the designed filters could maintain high timing performance. Consequently, the proposed plasmonic ultraviolet filter was suitable for maximizing the potential of barium fluoride scintillators.